<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <script>

        var count = 123;
        function fn() {
            console.log(count); // 234
        }
        function fun(num) {
            console.log(count); // 123
            function foo() {
                count = 234;
                console.log(count); // 234
                fn();
            }
            console.log(num); // 456
            foo()
        }

        fun(456);





    </script>

</body>

</html>